EVISION-720型移动式头部锥形束CT辐射剂量场空间分布特点分析

目的 探讨EVISION-720型移动式头部锥形束CT（简称EVISION-720型移动式CT）周围剂量当量率的检测方案并分析其辐射剂量场的空间分布特点。 方法 在0°（EVISION-720型移动式CT正前方）、45°、90°、135°、180°、225°、270°和315°逆时针分布的方向上，选取距地面0.3、0.8和1.3 m高度处的3个平面，以扫描中心为0点位置，分别在距离EVISION-720型移动式CT表面1~10 m处以等间隔1 m的方式布点。采用辐射剂量仪分别在110 kV/20 mA、90 kV/40 mA、70 kV/60 mA的额定参数下，测量距离EVISION-720型移动式CT表面6 m处的检测点位（临床应用时设置的操作位）的周围剂量当量率。在110 kV/20 mA额定参数下，测量所有检测点位的周围剂量当量率。在110 kV/20 mA额定参数下，以距地面0.3、0.8和1.3 m高度处的3个平面的测量结果，绘制1、5、10、20、40、100 μSv/h等剂量曲线，即辐射剂量场分布图。对在不同额定参数下，距地面相同高度处的周围剂量当量率，以及在相同额定参数下，距地面不同高度处的周围剂量当量率分别进行配对Wilcoxon秩和检验。 结果 在3种额定参数下，周围剂量当量率随管电压的增大逐渐增大，不随测量处距地面高度的变化而变化。3种额定参数中，110 kV/20 mA额定参数下0°方向上的周围剂量当量率最大，为（34.44±0.09） μSv/h。在不同额定参数下，距地面相同高度处的周围剂量当量率的差异均有统计学意义（Z=?2.527~2.524，均P<0.05）。在相同额定参数下，距地面不同高度处的周围剂量当量率的差异均无统计学意义（Z=?1.690~?0.169，均P>0.05）。EVISION-720型移动式CT辐射剂量场呈“对称性”和“三角形”分布:后方的2个45°方向，即135°和225°方向上的周围剂量当量率最低；正前方，即0°方向上的周围剂量当量率最高。 结论 EVISION-720型移动式CT辐射剂量场呈左右两侧“对称性”分布和前后“三角形”分布，前方的周围剂量当量率水平高于两侧和后方，医疗机构在使用时应加强对设备前方的辐射防护管理。

Analysis of spatial distribution characteristics of radiation dose field around EVISION-720 mobile head cone-beam CT

Objective To explore the detection scheme of ambient dose equivalent rates around EVISION-720 mobile head cone-beam CT (EVISION-720 mobile CT) and analyze the spatial distribution characteristics of its radiation dose field. Methods Three planes at a height of 0.3, 0.8, and 1.3 m from the floor were selected in the counterclockwise direction of 0° (in front of EVISION-720 mobile CT), 45°, 90°, 135°, 180°, 225°, 270°, and 315°. Using the scanning center as the zero-point position, the detection sites were arranged at a distance of 1–10 m from the surface of EVISION-720 mobile CT at an interval of 1 m. A radiation dosimeter was used to measure the ambient dose equivalent rates from the detection sites (operation sites set at the time of clinical application) at 6 m from the surface of EVISION-720 mobile CT under rated parameters of 110 kV/20 mA, 90 kV/40 mA, and 70 kV/60 mA. In addition, ambient dose equivalent rates were measured at all detection sites under rated parameter of 110 kV/20 mA. Measurements of the three planes at a height of 0.3, 0.8, and 1.3 m from the floor under rated parameter of 110 kV/20 mA were plotted for 1, 5, 10, 20, 40, and 100 μSv/h isodose curves, that is, radiation dose field distribution map. The Wilcoxon test was used for comparison among ambient dose equivalent rates at the same heights from the floor under the different rated parameters, and ambient dose equivalent rates at different heights from the floor under the same rated parameters, respectively. Results Under the three rated parameters, the measurement results of ambient dose equivalent rate gradually increase with the increase of tube voltage, but they do not change with the change of height from the floor. Moreover, the ambient dose equivalent rate in the 0° direction under rated parameter of 110 kV/20 mA was the highest ((34.44±0.09) μSv/h). At the same height from the floor under different rated parameters, the differences in ambient dose equivalent rates were statistically significant (Z=?2.527 to 2.524, all P<0.05). Furthermore, the differences in ambient dose equivalent rates at different heights from the floor under the same rated parameter are not statistically significant (Z=?1.690 to ?0.169, all P>0.05). Based on the radiation dose field of EVISION-720 mobile CT, the "symmetry" and "triangle" distribution are obtained: the ambient dose equivalent rate in the 135° and 225° direction was the lowest, and the ambient dose equivalent rate in the 0° direction was the highest. Conclusions The radiation dose field around EVISION-720 mobile CT presents a symmetry distribution on both sides and a triangle distribution in front and at back of the equipment. In addition, the ambient dose equivalent rate in the front is higher than that on both sides and at the back. Therefore, medical institutions should strengthen radiation protection management in front of the equipment.